1. Field of the Invention
This invention relates to a hot wire type air flow meter, and more particularly to an air flow meter which is suitable for measuring the flow rate of air supplied to an internal combustion engine and which operates with an excellent endurance electromagnetic compatibility.
2. Description of the Related Art
A hot wire type flow meter is disclosed in, for example, Japanese patent unexamined publication JP-A-No. 58-6414. In the prior art hot wire type flow meter, through-capacitors are fixed to conductor leading openings respectively of a sheilding case of an electrical conductive material accommodating a drive circuit which drives a flow rate sensor, and power supply and signal output conductors, to be connected to the drive circuit are extended into the shielding case through the respective through-capacitors thereby preventing the drive circuit from being disturbed by outside noises.
In the prior art flow meter described above, the power supply and signal output conductors connected to the drive circuit driving the flow rate sensor are electrically connected in an AC mode through the capacitors to the shielding case. However, no consideration is given in the prior art flow meter as to electrically connecting the conductive shielding case to a flow meter case in which the shielding case is mounted and the shielding case is merely fixed to the flow meter case by an adhesive. Therefore, the shielding case could not always be fixed to the flow meter case in a relation accurately positioned relative to the latter, and, because the former was not electrically connected to the latter, the endurance electromagnetic compatibility of the flow meter has been quite low.